* dcrt0.cc (get_cygwin_startup_info): Signal readiness when stracing since
strace::write_child relies on it. Use strace.activate to notify strace
process, passing in arg indicating whether we're forked.
* sigproc.cc (wait_sig): Accommodate new strace::activate argument.
* spawn.cc (child_info_spawn::worker): Oops. Previous suspended test was
actually correct. Revert and document.
* strace.cc (strace::activate): Send additional flag indicating whether this is
an attempt to activate a forked process.
(strace::hello): Report on windows pid.
* include/sys/strace.h (strace::strace): Make a dummy.
(strace::activate): Modify declaration to accept an argument.
(strace::write_childpid): Set regparm.
